Measurement of polymer moisture content and other polymer properties during the finishing process of polymer production is important to ensure that the product meets particular specifications. The measurement is particularly important for detecting grade switches, wherein production of one polymer having specific properties ends and production of another polymer having different properties begins. It is important to accurately detect the transition from the old grade to the new grade in order to properly label the product and reset the finishing plant controls for the new grade in a timely manner.
One of the previous methods of measuring polymer properties involves taking a sample from the process line and running tests in the laboratory. The major disadvantage of this approach is the long delay between taking the sample and receiving the results of the analysis. This delay can be at least one to two hours. The time delay leads to off-specification product, which, in turn, leads to less profit. The time delay also makes it difficult to optimize control of the process due to the delay in resetting the controls.
Another method of measuring polymer properties is the use of Fourier Transform Near-Infrared spectrometer (FTNIR) photometers. These devices permit measurement of moisture content while the polymer is on a conveyor line, but they do not allow for the measurement of other polymer properties. Photometer-based technology is also limited by its ability to provide a moisture value that only trends actual moisture variation in the polymer, rather than the highly accurate polymer moisture value resulting from the method of the present invention.
Yet another method of measuring polymer properties is the use of multi-wavelength dispersive-type spectrometers. These devices have been used on conveyor lines in a non-contact configuration, allowing for on-line measurements, but they provide inferior measurement accuracy and calibration stability as compared to the FTNIR spectrometer.
Prior methods of measuring polymer properties have either been inefficient due to time delays or have resulted in measurements that merely trend, rather than accurately measure, the value of the property. A need therefore exists for obtaining stable, accurate, real-time measurements of moisture content and other properties of polymers while the polymer is on the conveyor line.